Catalytic Converters

The catalytic converter is located in the exhaust system prior to the muffler. The catalytic converter is an emission control device added to the gasoline exhaust system to reduce hydrocarbon and carbon monoxide pollutants from the exhaust gas stream.

There are 3 types of catalytic converters: Conventional Oxidation Converters (COC), Three-Way Catalyst (TWC) and dual bed catalytic converters which are a combination of both the aforementioned. All catalytic converters are of 2 designs: a honeycomb-type block which is non-serviceable, or a small canister containing catalytic beads.

Both converters contain a base material of alumina impregnated with platinum/palladium, while three-way catalysts in addition to this also contain a material coated with platinum/rhodium. Both converters reduce hydrocarbons and carbon monoxide, while the TWC also reduces oxides of nitrogen.

NOTE: Use only unleaded fuel on vehicles equipped with a catalytic converter. If leaded fuel is used, coating and destruction of the catalytic surfaces will result and replacement is required.

On some models, a TWC is used in conjunction with a COC both contained in the same canister. Working in conjunction with this, there often is an air injection pipe. This pipe injects air between these 2 beds to help further oxidize the exhaust gases. This is called a dual-bed converter. See Fig 1 .

Fig 1: Cutaway View of Dual Bed Catalytic Converter

On most dual bed converter models, the first converter (3-way) in the exhaust system reduces hydrocarbons (HC) and carbon monoxide (CO), but mainly deals with oxides of nitrogen (NOx). In the second converter (oxidation type), with extra help from the air pump, reduction of hydrocarbons (HC) and carbon monoxide (CO) takes place.